把你的Press() 改成下面这样
function Press(){
var keyName = String.fromCharCode(window.event.keyCode);
alert("你敲击了 " + keyName);
}
<html>
<head>
<script>
function Press()
{
alert(window.event.keyCode);
if(window.event.keyCode==32)
{
alert("你敲击乐空格键。")
}
}
</script>
</head>
<body onload="alert('页面加载完成')"onunload="alert('你确定要关闭页面?')" onKeyPress="Press()">
</body>
</html>